1. 【-1/3xy的2次方】的2次方乘[xy【2x-y】+xy的2次方]；
= 【1/9x^2y^4】乘[2x^2y-2xy^2+xy^2]
= 【1/9x^2y^4】乘[2x^2y-xy^2]
= 2/9x^4y^5-1/9x^3y^6
2. 【-3x】的2次方-2【x-5】【x-2]
=9x^2-2x^2+4x+10x-20
=7x^2+14x-20
3. 【-2x-1/2】【x-1】；
=-2x^2+2x-1/2x+1/2
=-2x^2+3/2x+1/2
4. 【x-2】【x+3】-2x的2次方
=x^2+x-6-2x^2
=-x^2+x-6